Spatial distribution of cadmium concentrations in street dust in an arid environment

Abstract

Cadmium (Cd) concentration and its chemical speciation were studied in surface dust samples collected from 26 locations at Amman–Zarqa basin highways. The study area represents a heavily trafficked arid environment associated with highly calcareous soils with an average of 53 % CaCO3; such combination gives the investigation further speculations on abundant Cd bonded forms. Sequential extraction technique (SET) was used to assess the exchangeable, bound to carbonates, bound to iron oxide, bound to organic matter, and residual fractions in surface dust samples. Total and fractional Cd spatial distributions were spatially investigated and utilized to generate Cd contamination factor map. Total Cd concentrations ranged between 4.1 and 17.9 mg/kg where maximum contamination was allocated at the study area center. The exponential behavior of Cd distribution in space gave further distinction of the possible contamination sources. The main Cd speciation was in the following order: bound to iron oxide > residual > exchangeable > bound to carbonate > bound to organic matter. The degree of surface contamination was determined by individual contamination factor that delineated those areas located close to the wastewater treatment plant that had high potential risk to fauna and flora. Relationship between the total and fractional Cd concentrations with soil chemical properties showed that pH, CEC, and amorphous Fe were positively related to total extracted Cd, while carbonate content and OM are negatively correlated with Cd.